1. Field of the Invention
The invention relates to superalloy articles and methods for producing superalloy articles.
2. Description of the Prior Art
Nickel base superalloys have been widely developed in the last 40 years, and an extensive amount of literature exists describing such alloys. The book "The Superalloys," edited by Sims and Hazel, published by Wiley in 1972 summarizes the field.
The conventional nickel base superalloys are based on nickel with additions of aluminum and other elements to form a gamma prime strengthening phase. The microstructure of nickel base superalloys consists of a gamma matrix (a nickel solid solution) containing from about 15 to about 60 volume percent of the gamma prime phase. (The gamma prime phase is an ordered compound based on Ni.sub.3 Al). Numerous alloy additions may be made to the basic alloy for a variety of reasons. Titanium is often added and acts interchangeably with the aluminum as a gamma prime former. Chromium is commonly added to improve oxidation resistance. Refractory metals such as molybdenum, tungsten, tantalum and columbium may be added for solid solution strengthening. Cobalt is often added to control the gamma prime solvus temperature and improve the hot workability.
There is a general correlation between strength and gamma prime content, the high gamma prime alloys have the best mechanical properties. The truly high strength superalloys are commonly used in the cast state since their high strength does not permit them to be formed except by casting.